1. Technical Field
The invention relates to a method for filling containers with piece goods, as recited in the preamble to claim 1.
2. Description of the Prior Art
Piece goods, which are delivered from production systems via supply conveyors to a packaging line can be placed into the provided containers in a fully automatic fashion by means of robots. EP 0 250 470 has disclosed robots of this kind, also referred to as pickers or delta robots, which are suitable for use in packaging lines. It concerns a robot with a base body, which is linked by means of three two-part arms to a working part on which grippers or suction elements are provided. U.S. Pat. No. 6,543,987 and U.S. Pat. No. 6,896,473 have disclosed further developments in which the delta robot has a fourth axis that can be changed in length. In lieu of delta robots, there are also other suitable pick & place robots, for example the so-called Scara robot or the 6-axis robot.
Usually, piece goods and containers are transported on two or more supply conveyors extending parallel to one another; as the conveyors move continuously or incrementally, the pickers pick up the piece goods individually or in groups and place them into the containers.
EP 0 749 902 A describes a system in which the piece goods and the containers are transported in a parallel flow, i.e. parallel and in the same direction to each other. EP 0 865 465 A discloses a system using the counterflow principal, i.e. the container conveyors do in fact extend parallel to the piece goods conveyor, but in the opposite direction from the conveying direction of the piece goods conveyor.
EP 1 285 851 A proposes a method for increasing the service life and maximum duration of use of picker robots that are used along such picker lines, employing the parallel flow or counterflow principal. To accomplish this, the robots are controlled as a function of the arrangement of piece goods on the supply conveyor so that they are utilized as consistently as possible and are not subjected to intense power fluctuations.
In EP 1 352 831 A, the relative speed between the supply of the containers and the supply of the piece goods is controlled in the region of the picker line. The control of the relative speed here is carried out as a function of a fill level of at least one storage element. This method permits an efficient transfer of piece goods into containers while also assuring the most complete possible filling.
All of these methods, however, concern the normal operation of the system. It is always assumed that enough piece goods are supplied and that a shortage is rectified as soon as possible. At the end of production, e.g. in the event of a product change or format change, but also when the system is being cleaned or in the event of an unexpected breakdown in the piece goods production system, there are too few piece goods waiting on the supply conveyor to allow all of the containers on the container conveyor to be filled completely. Usually, the problem lies in the fact that at the time that the production process is stopped, the number of products still on the piece goods conveyor does not coincide with the number of placement positions or slots that remain to be filled in the container. But with the counterflow principal in particular, which also involves the products “traveling away” from the containers that remain to be filled, many of the containers are already partially filled. It is then no longer possible to fill these partially filled containers.
In the final control, incompletely filled containers are separated out as insufficiently meeting quality requirements, usually by means of a scale, and must be filled by hand or disposed of as waste. In addition, the last piece goods remaining on the piece goods conveyor must be cleared out by hand and disposed of. The quantity of rejected product is not insignificant. This also requires a sufficient amount of available personnel. If critical piece goods such as sponge cakes are being packaged, then it is not permissible for the partially filled containers to remain unprocessed for too long. This changeover procedure is time-consuming, particularly with frequent product changes, and reduces the productivity of the system.